Luminaires are often placed in service in industrial applications which subject the luminaire to severe weathering conditions or extremely corrosive atmospheres. Conventionally, luminaires exposed to such conditions have been comprised of housings fabricated of die-cast aluminum, steel, brass or stainless steel. However, even these materials, when used in some extremely corrosive applications are not entirely satisfactory and, accordingly, the life of the luminaire is limited. While various paints or epoxy coatings have been tried in an effort to extend the life of the luminaire, these attempts have also proven to be less than entirely satisfactory.
While substitutions of other materials, such as plastic, for the metallic materials conventionally used in the external housing of heavy-duty luminaires, can provide suitable resistance to corrosive atmospheres, the shift to plastics has been slow because of the necessity of utilizing a housing material capable of supporting the heavy electrical and optical components of the luminaire. Since these components have usually been mounted to and supported by the luminaire housing, the use of more economical but weaker materials has not been widely adopted. Moreover, regulations of organizations such as Underwriters Laboratories recognize the limited stress bearing capabilities of non-metallic housings and prescribe various safety measures which must be employed when heavy electrical or optical components are mounted on and supported by a non-metallic housing. These measures add cost to the luminaire.
Various attempts have been used to employ plastic housings in heavy duty luminaires. For example, U.S. Pat. No. 4,388,680 describes a luminaire having a plastic outer housing and an inner base plate which carries the load of some of the heavy electrical components. However, the structure described in this patent nonetheless still relies on the plastic housing to carry the load of the luminaire lamp and socket assembly and the load of the refractor assembly. Should the plastic housing fail during the life of the luminaire nothing described in this patent provides for retention of these components to the luminaire. Accordingly, it is possible for these components to fall from the luminaire upon failure of the plastic housing. This possibility exists because the luminaire fails to provide for either mounting of the refractor assembly and the lamp and socket assembly on a metallic portion of the luminaire or for back-up or supplemental means of supporting these assemblies.
It is also observed that the structure described in the aforementioned patent retains the two plastic housing members in mating engagement with each other by the use of a hinge and latch each located exterior to the housing members. Thus, the hinge and latch are exposed to corrosive atmospheres that might be present in the environment. Should extensive corrosion occur, the latch or hinge may fail resulting in separation of the housing members.
Another device known in the prior art to utilize plastic outer housings is as described in U.S. Pat. No. 4,379,321. However, like the structure described in the patent previously mentioned, the luminaire plastic housing carries the load of both the refractor and lamp and socket assemblies and retains the housing members in mating engagement by a hinge and latch (screws)disposed external to the housing.
Where component assemblies of a luminaire are of a weight in excess of Underwriter Laboratories limits, various supplemental, or back-up, support means must be employed for safety purposes. One such safety means employed in the past is the provision of a loose chain or cable which is separate from but connected to a metallic portion of the support structure of the luminaire and which captures those components having the aforementioned excess weight. Thus, if the plastic housing should have a stress-induced or other failure, the separate safety chain or cable prevents the luminaire from falling. However, the use of a separate loose chain or cable introduces additional cost and can produce a hazard if the separate loose chain were to contact current conducting components within the luminaire.